480 



BELL SYSTEM TECHNICAL JOURNAL 



The high peak on the left represents the cross-section-in-azimuth of 

 the beam shown in Fig. 2. Two similar peaks mark the positions of 

 companion beams which w^ith the first form a set of three, as required 

 by the threefold symmetry of the crystal about its (11 1) directions — the 

 direction of the incident beam. The lesser intermediate peaks are due 

 to a different set of beams which is not here fully developed. 



A 



A 



B 



A 



Fig. 3 — Curve showing intensity of elastic scattering of 54-volt primary beam as 

 function of azimuth for latitude of peak in 54-volt curve, Fig. 2. 



The de Broglie relation was tested by computing wave-lengths 

 from the angles of the diffraction beams and the known constant of the 

 crystal, and comparing these with corresponding wave-lengths com- 

 puted from the formula X = h/p, where p, the momentum of the elec- 

 trons, was obtained from the potential used to accelerate the beam and 

 the known value of e/m for electrons. If wave-lengths computed from 

 the formula agreed with those obtained from the diffraction data, the 

 de Broglie relation would be verified. How nearly the theoretical 

 values agreed with the experimental is illustrated in Fig. 4. For perfect 

 agreement all points would fall on the line drawn through the origin. 



You will realize without my telling you that this series of experiments 

 extending in time over a period of eight or nine years and requiring the 

 construction and manipulation of intricate apparatus w^as not made by 

 me alone. From first to last a considerable number of my colleagues 

 contributed to the investigation. Chief among these were my two 

 exceptionally able collaborators. Dr. C. H. Kunsman and Dr. L. H. 

 Germer. Dr. Kunsman worked with me throughout the early stages 

 of the investigation, and Dr. Germer, to whose skill and perseverance 



